1. Field of the Invention
The present invention relates to a process for producing a monoester from dicarboxylic acid fluoride, and more particularly to a process for producing monoester monoacid fluoride of dicarboxylic acid useful as a starting material for synthesis of perfluorovinyl ether from dicarboxylic acid fluoride.
2. Related Art
Perfluorovinyl ether is a useful monomer for use in fluorine-containing elastomers, etc. and its synthesis is carried out by converting the acid fluoride group of monoester monoacid fluoride of dicarboxylic acid to a carboxylic acid salt, followed by thermal decomposition reaction (JP-B-53-33572 and 53-33573). 
Monoester monoacid fluoride of dicarboxylic acid for this purpose can be obtained usually by allowing dicarboxylic acid fluoride to react with an equimolar amount of alcohol, thereby esterifiying the acid fluoride group on one side. In that case, selectivity will be increased in a lower molar ratio of alcohol as a reactant, but a larger amount of unreacted dicarboxylic acid fluoride will remain, resulting in poor conversion. On the other hand, the conversion will be increased in a higher molar ratio of alcohol as a reactant, but the yield of diester will be increased, resulting in poor selectivity.
An object of the present invention is to provide a process for producing monoester monoacid fluoride of dicarboxylic acid from dicarboxylic acid fluoride with higher conversion and selectivity, resulting in higher yield.
The object of the present invention can be attained according to a process for producing monoester monoacid fluoride of dicarboxylic acid, which comprises allowing a dicarboxylic acid fluoride represented by the following general formula:
FOCCF(CF3)OCF2(A)p(CF)qCOF
where A is a bifunctional perfluorinated group having 1 to 10 carbon atoms; p is 0 or 1; and q is an integer of 1 to 10, to react with an alcohol having at least 3 carbon atoms, thereby esterifying the terminal CF2COF group.
JP-B-57-61339 discloses that asymmetrical dicarboxylic acid fluoride represented by the foregoing general formula can be obtained by allowing dicarboxylic acid fluoride represented by the following general formula:
FOC(A)p(CF2)qCOF
to react with hexafluoropropylene oxide (U.S. Pat. No. 3,114,778) or by allowing perfluorolactone to react with hexafluoropropene oxide (JP-A-53-3017), where A is a branched or unbrached bifunctional perfluorinated group capable of containing one or more ether bonds, represented e.g. by the following general formula:
[CF(CF3)OCF2]m(Rf)nxe2x80x94
Rf: Straight or branched perfluoroalkylene group having 1 to 10, preferably 1 to 4 carbon atoms
m: 0, 1 or 2
n: 0 or 1
Dicarboxylic acid fluoride includes, for example, the following compound:
FOCCF(CF3)OCF2COF
FOCCF(CF3)O(CF2)2COF
FOCCF(CF3)O(CF2)3COF
FOCCF(CF3)O(CF2)4COF
FOCCF(CF3)O(CF2)5COF
FOCCF(CF3)OCF2CF(CF3)OCF2COF
FOCCF(CF3)OCF2CF(CF3)O(CF2)2COF
FOCCF(CF3)OCF2CF(CF3)O(CF2)3COF
FOCCF(CF3)OCF2CF(CF3)O(CF2)4COF
FOCCF(CF3)OCF2CF(CF3)O(CF2)5COF
Alcohols for use in the reaction with these dicarboxylic acid fluorides include, for example, alcohols having at least 3 carbon atoms, such as propanol, isopropanol, n-butanol, isobutanol (2-butanol), 2-methyl-1-propanol, 4-heptanol, 2,2-dimethyl-1-propanol, 2,4-dimethyl-3-pentanol, etc. Above all, alcohols with a branched group are preferable.
Reaction is carried out between one part by mole of dicarboxylic acid fluoride and 0.7-2 parts by mole, preferably about 1- about 1.5 parts by mole, of an alcohol at a reaction temperature of about xe2x88x9260xc2x0 to about 60xc2x0 C. Selectivity can be increased at a lower reaction temperature, but from the viewpoint of cooler capacity, economy, etc. a reaction temperature of about xe2x88x9240xc2x0 to about 20xc2x0 C. is preferable. Reaction can be carried out in the presence of a solvent. A any solvent can be used, so long as it will not inhibit the reaction. Diglyme, tetraglyme, etc. used in the synthesis of dicarboxylic acid fluoride are preferable as solvents. Hydrogen fluoride, which is a by product of condensation reaction, is adsorbed onto an alkali metal fluoride such as sodium fluoride, etc. added to the reaction system as an acid-removing agent, and thus corrosion, etc. of reactors can be prevented.
Copolymers obtained by copolymerization with perfluorovinyl ether can be effectively used as functional, fluorine-containing polymers in the field of water- and oil-repellents, etc. Monoester monoacid fluoride of dicarboxylic acid having a perfluoroether bond, FOCCF(CF3)OCF2(A)p(CF2)qCOOR, which is an intermediate for the synthesis of perfluorovinyl ether as a component for such copolymers, can be produced with good conversion and selectivity by using an alcohol having at least 3 carbon atoms as an esterifying agent.
Selective monoesterification reaction of such a asymmetrical dicarboxylic acid difluoride can be effectively used for separation and purification of a mixture of dicarboxylic acid difluoride isomers which comprises symmetrical dicarboxylic acid difluoride and asymmetrical dicarboxylic acid difluoride.
By allowing dicarboxylic acid difluoride represented by the following general formula [A]:
FOCCF(CF3)O(CF2)n+2OCF(CF3)COFxe2x80x83xe2x80x83[A]
to react with an alkali metal carbonate such as sodium carbonate, potassium carbonate, etc., a perfluorodivinyl ether represented by the following formula can be synthesized:
CF2xe2x95x90CFO(CF2)n+2OCFxe2x95x90CF2
Dicarboxylic acid difluoride [A] can be synthesized by allowing dicarboxylic acid difluoride represented by the following general formula:
xe2x80x83FOC(CF2)nCOF
to react with hexafluoropropene oxide (U.S. Pat. No. 3,114,778), but dicarboxylic acid difluoride represented by the following general formula [B] is inevitably by-product at the same time:
FOCCF(CF3)OCF2CF(CF3)O(CF2)n+1COFxe2x80x83xe2x80x83[B]
These dicarboxylic acid difluorides [A] and [B] are isomers with the same molecular weight and with no substantial difference in boiling point, and thus are very difficult to separate from each other by ordinary distillation procedures.
The foregoing selective monoesterification reaction of the present invention can be effectively used for efficient separation and purification of only desired dicarboxylic acid difluoride from a mixture of dicarboxylic acid difluoride isomers with the same molecular weight and with no substantial difference in boiling point.
That is, a mixture of dicarboxylic acid difluoride isomers, which comprises an isomer represented by the following general formula [A]:
FOCCF(CF3)O(CF2)n+2OCF(CF3)COFxe2x80x83xe2x80x83[A]
where n is 0 or an integer of 1 or more, and an isomer represented by the following general formula [B]:
FOCCF(CF3)OCF2CF(CF3)O(CF2)n+1COFxe2x80x83xe2x80x83[B]
where n is 0 or an integer of 1 or more, is allowed to react with a branched alcohol having at least 3 carbon atoms, thereby monoesterifying the terminal CF2COF group of isomer [B], and then isomer [A] is separated and purified therefrom by distillation and obtained as desired dicarboxylic acid difluoride.
Alcohols for use in the monoesterification of terminal carboxylic acid fluoride group of the isomer mixture comprising dicarboxylic acid difluorides [A] and [B] include, for example, branched alcohols having at least 3 carbon atoms such as 2-propanol, 2-methyl-1-propanol, 4-heptanol, 2,2-dimethyl-1-propanol, 2,4-dimethyl-3-pentanol, etc.
In the monoesterification reaction with a branched alcohol of such a stereoselectivity, monoesterification reaction of asymmetrical dicarboxylic acid difluoride [B] takes place preferentially, thereby facilitating separation of dicarboxylic acid difluoride [A] from [B] by distillation procedures. In the case of using an alcohol having one or two carbon atoms or an unbranched alcohol having even at least 3 carbon atoms, monoesterification reaction of dicarboxylic acid fluorides [A] and [B] takes place substantially in parallel, resulting in decreased recovery rate of dicarboxylic acid difluoride [A].
Monoesterification reaction of asymmetrical dicarboxylic acid difluoride [B] can be carried out at a reaction temperature of about xe2x88x9260xc2x0 to about 60xc2x0 C. with 0.5-10 parts by mole, preferably about 1 to about 4 parts by mole, of an alcohol per part by mole of isomer [B]. Selectivity can be increased at a lower reaction temperature, but from the viewpoint of cooler capacity, economy, etc., a reaction temperature of about xe2x88x9240xc2x0 to about 20xc2x0 C. is preferable. Reaction can be carried out in the presence or the absence of a solvent. Any solvent can be used, so long as it will not inhibit the reaction. Diglyme, tetraglyme, etc. used in the synthesis of dicarboxylic acid difluoride are preferable as solvents. Hydrogen fluoride, which is a by product of condensation reaction, is adsorbed onto an alkali metal fluoride such as sodium fluoride, etc. added to the reaction system as an acid-removing agent, and thus corrosion, etc. of reactors can be prevented.
A mixture of monoesterified dicarboxylic acid difluoride isomers is a mixture comprising dicarboxylic acid difluorides [A] and [B], and their monoesterified compounds. Complete monoesterification of dicarboxylic acid difluoride [B] can be attained by using much more alcohol than isomer [B], but elimination of dicarboxylic acid difluoride [B] by the complete monoesterification of [B] will lower the recovery rate of dicarboxylic acid difluoride [A]. Thus, it is necessary to restrict the monoesterification of dicarboxylic acid difluoride [B] to about 80%, thereby maintaining an appropriate recovery rate of dicarboxylic acid difluoride [A].
In the mixture of monoesterified dicarboxylic acid disulfide isomers comprising the foregoing components, a considerable proportion of dicarboxylic acid difluoride [B] is monoesterified, and thus dicarboxylic acid difluoride [A] can be separated and purified with a high purity from the mixture by distilling the mixture under atmospheric or subatmospheric conditions.
In other words, dicarboxylic acid difluoride can be obtained as a mixture of isomers with no substantial difference in boiling point by reaction of FOC(CF2)nCOF with hexafluoropropene oxide, and a dicarboxylic acid difluoride isomer useful for an intermediate to synthesis of perfluorodivinyl ether can be obtained easily with a high purity by monoesterification of the isomer mixture with a specific branched alcohol, followed by distillation of the monoesterified isomer mixture.